The poem starts with a striking claim: dust, something we usually barely notice, is "great" and is "made in the country." It sounds almost like a product with a place of origin. The speaker then says nothing is cheaper for filling "the house and urn," and that pairing is the heart of it. A house is where we live, an urn is where ashes go after death, and dust is what connects them. Ordinary household grime and human remains become the same cheap material.
The last lines turn uncertain. The speaker fills these spaces "with I know not yet / what sleep," which seems to borrow from Hamlet's worry about what dreams may come in death's sleep. Judging by the imagery, the speaker feels a quiet unease rather than panic. The mood is hushed, a little dry and wry, and thoughtful. Death is treated as plain and everywhere, yet still a mystery, and the short, broken lines leave us hovering in that not-knowing.